Compounds for a liquid-crystalline medium, and the use thereof for high-frequency components

ABSTRACT

The present invention relates to 1,4-diethynylbenzene derivatives having substituents in the 2,3-position (cf. formula I, Claims), to the use thereof for high-frequency components, to liquid-crystalline media comprising the compounds, and to high-frequency components, in particular antennae, especially for the gigahertz range, comprising these media. The liquid-crystalline media serve, for example, for the phase shifting of microwaves for tuneable ‘phased-array’ antennae.

The present invention relates to 1,4-diethynylbenzene derivatives havingsubstituents in the 2,3-position of the benzene ring (cf. formula I,Claims), to the use thereof for high-frequency components, toliquid-crystalline media comprising the compounds, and to high-frequencycomponents, in particular antennae, especially for the gigahertz range,comprising these media. The liquid-crystalline media serve, for example,for the phase shifting of microwaves for tuneable ‘phased-array’antennae.

Liquid-crystalline media have been used for some time in electro-opticaldisplays (liquid crystal displays—LCDs) in order to display information.

1,4-Diethynylbenzene derivatives are proposed as liquid-crystallinecomponents in the specifications EP 0968988 A1, DE 19907941 A1, DE10120024 A1 and JP 08012599A. However, the specific substitution thereindoes not correspond to the substitution pattern of the compoundsreproduced in the context of this invention.

However, liquid-crystalline media have recently also been proposed foruse in components for microwave technology, such as, for example, in DE10 2004 029 429 A and in JP 2005-120208 (A).

An industrially valuable application of liquid-crystalline media inhigh-frequency technology is based on their property that theirdielectric properties can be controlled by a variable voltage,particularly for the gigahertz range. Thus, tuneable antennae can bedesigned which contain no moving parts (A. Gaebler, A. Moessinger, F.Goelden, et al., “Liquid Crystal-Reconfigurable Antenna Concepts forSpace Applications at Microwave and Millimeter Waves,” InternationalJournal of Antennas and Propagation, vol. 2009, Article ID 876989, 7pages, 2009. doi:10.1155/2009/876989).

The publication A. Penirschke, S. Müller, P. Scheele, C. Weil, M.Wittek, C. Hock and R. Jakoby: “Cavity Perturbation Method forCharacterization of Liquid Crystals up to 35 GHz”, 34^(th) EuropeanMicrowave Conference—Amsterdam, 545-548, describes, inter alia, theproperties of the known, liquid-crystalline single substance K15 (MerckKGaA, Germany) at a frequency of 9 GHz.

1-(Phenylethynyl)tolans, also called bistolan compounds below, having analkyl substitution on the central phenylene ring are known to the personskilled in the art. For example, the publication S.-T. Wu, C.-S. Hsu,K.-F. Shyu Appl. Phys. Lett. (1999), 74 (3), 344-346, discloses variousliquid-crystalline bistolan compounds having a lateral methyl group, ofthe formula

Besides liquid-crystalline bistolan compounds of this type having alateral methyl group, C. S. Hsu, K. F. Shyu, Y. Y. Chuang, S.-T. Wu Liq.Cryst. (2000), 27 (2), 283-287, also discloses corresponding compoundshaving a lateral ethyl group and proposes the use thereof, inter alia,in “liquid crystal optically phased arrays”.

DE 10 2004 029 429 A (cf. above) describes the use of conventionalliquid-crystal media in microwave technology, inter alia in phaseshifters. Liquid-crystalline media have already been investigatedtherein with respect to their properties in the corresponding frequencyrange.

However, the compositions or individual compounds known to date aregenerally afflicted with disadvantages. Most of them result, besidesother deficiencies, in disadvantageously high losses and/or inadequatephase shifts or inadequate material quality.

For use in high-frequency technology, liquid-crystalline media havingparticular, hitherto rather unusual, non-standard properties, orcombinations of properties, are required.

Thus, novel components for liquid-crystalline media having improvedproperties are necessary. In particular, the loss in the microwave rangemust be reduced and the material quality (η) must be improved. Fortuneable antennae, liquid-crystalline media having a fast reaction timeto a change in the voltage between the electrodes of the cell are alsorequired.

In addition, there is a need to improve the low-temperature behaviour ofthe components. Both an improvement in the operating properties and alsoin the shelf life is necessary here.

There is therefore a considerable demand for liquid-crystalline mediahaving suitable properties for corresponding practical applications.

Surprisingly, it has been found that the compounds according to theinvention having two substituents in the ortho position on one aromaticring have a significantly higher clearing point (transition from thenematic phase into the isotropic phase) compared with a correspondingmonosubstituted compound or a disubstituted compound in which thesubstituents are not arranged in the ortho position to one another. Atthe same time, the rotational viscosity (γ₁) is significantly lower thanin the comparative compounds having fewer substituents or without anortho position of the substituents. This effect arises in compounds inwhich the ring systems are kept at distance by rigid ethynylene bridges.Utilising this effect, it has now been found, surprisingly, thatliquid-crystalline media having a suitable, nematic phase range and highΔn which do not have the disadvantages of the materials of the prior artor at least only do so to a considerably reduced extent can be achievedwith the compounds according to the invention.

The invention relates to compounds of the formula I,

-   in which-   A³ denotes

-   L¹, L² each, independently of one another, denote branched or    unbranched alkyl, alkenyl or alkynyl having 1 to 12 C atoms, in    which, in addition, one or more “—CH₂—” groups may be replaced,    independently of one another, by O, substituted or unsubstituted    cycloalkyl, cycloalkenyl, substituted or unsubstituted phenyl,    substituted or unsubstituted arylethynyl, fluorinated alkyl or    alkenyl, fluorinated alkoxy or alkenyloxy, F, Cl, Br, CN, NCS or    SF₅,-   L³, L⁴ are defined like L^(1/2) or denote H,-   R¹ and R², independently of one another, denote a halogenated or    unsubstituted alkyl radical having 1 to 15 C atoms, where, in    addition, one or more CH₂ groups in these radicals may each be    replaced, independently of one another, by —C≡C—, —CH═CH—, —CF═CF—,    —CF═CH—, —CH═CF—, —(CO)— and —O— in such a way that O atoms are not    linked directly to one another,    -   F, Cl, Br, CN, CF₃, OCF₃, NCS or SF₅,    -   R² also denotes H,-   A¹, A², A⁴, A⁵ each, independently of one another, denote    -   a) 1,4-phenylene, in which one or more, preferably one to two,        CH groups may be replaced by N,    -   b) trans-1,4-cyclohexylene or cyclohexenylene, in which, in        addition, one or two non-adjacent CH₂ groups may be replaced by        —O— and/or —S—, and in which H may be replaced by F,    -   c) a radical of the formula

-   -   or    -   d) a radical from the group 1,4-bicyclo[2.2.2]octylene,        cyclo-butane-1,3-diyl, spiro[3.3]heptane-2,6-diyl,        thiophene-2,5-diyl, thiophene-2,4-diyl, furan-2,5-diyl,        furan-2,4-diyl,

-   -   and in which, in groups a), b), c) and d),    -   one or more H atoms may, in addition, be replaced by Br, Cl, F,        CN, —NCS, —SCN, SF₅, C₁-C₁₀ alkyl, C₁-C₁₀ alkoxy or a mono- or        polyfluorinated C₁-C₁₀ alkyl or alkoxy group,    -   and where    -   at least one radical from A¹ to A⁵, preferably from A², A³ and        A⁴, represents a radical according to a),

-   k denotes 0 or 1,

-   Z¹, Z⁵, independently of one another, denote a single bond, —C≡C—,    —CH═CH—, —CH₂O—, —(CO)O—, —CF₂O—, —CF₂CF₂—, —CH₂CF₂—, —CH₂CH₂—,    —(CH₂)₄—, —CH═CF— or —CF═CF—, where asymmetrical bridges may be    oriented to both sides,

-   where, for k=0, Z⁵ denotes a single bond, and

-   m, n, independently of one another, denote 0, 1 or 2.

The compounds according to the invention have a high clearing point, alow melting point, extremely high optical anisotropy (Δn). Fast responsetimes are achieved by a surprisingly low rotational viscosity γ₁. Aphase shifter can thus adjust faster. The relatively low loss factor inthe microwave spectrum is also advantageous. The compounds, alone or ina mixture with further mesogenic components, have a nematic phase over abroad temperature range. These properties make them particularlysuitable for use in components for high-frequency technology, inparticular in liquid-crystalline phase shifters. Liquid-crystallinemedia according to the invention have the corresponding properties, forexample a broad phase range, fast response time, and in addition goodlow-temperature stability.

Preferred compounds of the formula I are characterised by the choice ofone or more of the following parameters:

-   -   The index m is preferably 0 or 1, particularly preferably 0. The        index n is preferably 0 or 1, particularly preferably 0. m+n is        preferably 0 or 1.    -   The ring groups A¹ and A⁵ are, independently of one another,        preferably a 1,4-phenylene, in which, in addition, one or more H        atoms may be replaced by Br, Cl, F, CN, alkyl (C₁-C₁₀), methoxy        or a mono- or polyfluorinated methyl or methoxy group.    -   The bridging groups Z¹ and Z⁵ are, independently of one another,        preferably a single bond, —C≡C—, —CF═CF— or —CH═CH—,        particularly preferably a single bond.

Preferred structures are therefore selected from I-1 to I-3:

One of the radicals R¹ or R², preferably R¹, preferably denotes astraight-chain alkyl radical having 1 to 15 C atoms, where, in addition,one or more CH₂ groups in these radicals may each be replaced,independently of one another, by —C≡C—, —CH═CH—, —(CO)O—, —O(CO)—,—(CO)—, —O— in such a way that O atoms are not linked directly to oneanother. The groups R¹ and R² are preferably both an alkyl having 2 to 7C atoms. In this case, R¹ and R² denote, for example, propyl and hexylor butyl and butyl, furthermore propyl and pentyl, propyl and hexyl orbutyl and pentyl.

The groups L¹ and L² preferably each, independently of one another,denote F, Cl, CN, branched or unbranched alkyl, alkenyl or alkynylhaving 1 to 8 C atoms, in which, in addition, one or more “—CH₂—” groupsmay be replaced, independently of one another, by O, substituted orunsubstituted cycloalkyl, cycloalkenyl, fluorinated alkyl or alkenyl,fluorinated alkoxy or alkenyloxy, each having up to 8 C atoms,particularly preferably F, Cl, alkyl having 1 to 5 C atoms, alkenylhaving 2 to 5 C atoms, cyclopropyl or cyclobutyl. Preferably, one groupfrom L^(1/2) is an F, methyl, ethyl, cyclopropyl or Cl, particularlypreferably F, and the other group is as defined above, or is preferablyF, Cl, alkyl having 1 to 5 C atoms, alkenyl having 2 to 5 C atoms,cyclopropyl or cyclobutyl.

The groups L³ and L⁴ are preferably both H or both not H, particularlypreferably are both H.

The ring group A³ preferably has a part-structure selected from thefollowing formulae:

Preferred embodiments of the invention are therefore selected from thefollowing illustrative structures:

in which R¹ and R² independently denote an alkyl radical having 2 to 7 Catoms, for example a propyl or hexyl radical or each denote a propyl,butyl, pentyl or hexyl radical.

For compounds of the formula I in which k=0, Z⁵ denotes a single bond.For compounds of the formula I in which k=0, the variable n furthermorepreferably adopts the value 0, and the radical R² preferably denotes ahalogenated or unsubstituted alkyl radical having 1 to 15 C atoms,where, in addition, one or more CH₂ groups in this radical may each bereplaced, independently of one another, by —C≡C—, —CH═CH—, —CF═CF—,—CF═CH— and —CH═CF—, or denotes CN, CF₃, NCS or SF₅. R² in thesecompounds particularly preferably denotes an unsubstituted alkyl radicalhaving 1 to 15 C atoms, CN or NCS.

The compounds of the formula I can advantageously be obtained inaccordance with the following general reaction schemes (Reaction SchemesI to VIII). The parameters R^(1/2), A¹⁻⁵, Z^(1/5), m and n therein areas defined above and below. R has the meaning of R^(1/2).

In Reaction Schemes III to VII, the synthesis of variously substitutedrings A³ is reproduced. The phenylalkynyl radicals here can begeneralised to any desired radicals —≡-A²-(Z¹-A¹)_(m)-R¹ or—≡-(A⁴)_(k)-(Z⁵-A⁵)_(n)-R².

The liquid-crystalline media in accordance with the present inventioncomprise one or more compounds of the formula I and optionally at leastone further, preferably mesogenic compound. The liquid-crystal mediumtherefore preferably comprises two or more compounds which arepreferably liquid-crystalline. Preferred media comprise the preferredcompounds of the formula I.

Further components of the liquid-crystalline media are preferablyselected from the compounds of the formula II:

-   in which-   L¹¹ denotes R¹¹ or X¹¹,-   L¹² denotes R¹² or X¹²,-   R¹¹ and R¹², independently of one another, denote unfluorinated    alkyl or unfluorinated alkoxy having 1 to 17, preferably having 3 to    10, C atoms or unfluorinated alkenyl, unfluorinated alkynyl,    unfluorinated alkenyloxy or unfluorinated alkoxyalkyl having 2 to    15, preferably 3 to 10, C atoms, preferably alkyl or unfluorinated    alkenyl,-   X¹¹ and X¹², independently of one another, denote F, Cl, Br, —CN,    —NCS, —SCN, —SF₅, fluorinated alkyl or fluorinated alkoxy having 1    to 7 C atoms or fluorinated alkenyl, fluorinated alkenyloxy or    fluorinated alkoxyalkyl having 2 to 7 C atoms, preferably    fluorinated alkoxy, fluorinated alkenyloxy, F or Cl,-   p, q independently denote 0 or 1,-   Z¹¹ to Z¹³, independently of one another, denote trans-CH═CH—,    trans-CF═CF—, —C≡C— or a single bond, and

-   -   independently of one another, denote

-   -   where R¹³ denotes Cl, C₁₋₅ alkyl, C₁₋₅ alkenyl or C₃₋₆        cycloalkyl.

In a preferred embodiment of the present invention, theliquid-crystalline media comprise one or more compounds of the formula Iand one or more compounds of the formula II.

The liquid-crystalline media in accordance with the present applicationpreferably comprise in total 5 to 95%, preferably 10 to 90% andparticularly preferably 15 to 80%, of compounds of the formula I.

The liquid-crystalline media in accordance with the present inventionpreferably comprise, more preferably predominantly consist of, even morepreferably essentially consist of and very preferably completely consistof compounds selected from the group of the compounds of the formulae Iand II.

In this application, “comprise” in connection with compositions meansthat the entity in question, i.e. the medium or the component, comprisesthe component or components or compound or compounds indicated,preferably in a total concentration of 10% or more and very preferably20% or more.

In this connection, “predominantly consist of” means that the entity inquestion comprises 55% or more, preferably 60% or more and verypreferably 70% or more, of the component or components or compound orcompounds indicated.

In this connection, “essentially consist of” means that the entity inquestion comprises 80% or more, preferably 90% or more and verypreferably 95% or more, of the component or components or compound orcompounds indicated.

In this connection, “completely consist of” means that the entity inquestion comprises 98% or more, preferably 99% or more and verypreferably 100.0%, of the component or components or compound orcompounds indicated.

The liquid-crystalline media in accordance with the present applicationpreferably comprise in total 10 to 100%, preferably 20 to 95% andparticularly preferably 25 to 90%, of compounds of the formulae I andII.

In accordance with the present invention, the compounds of the formulaII are preferably used in a total concentration of 10% to 90%, morepreferably 15% to 85%, even more preferably 25% to 80% and verypreferably 30% to 75%, of the mixture as a whole.

In addition, the liquid-crystalline media may comprise furtheradditives, such as stabilisers, chiral dopants and nanoparticles. Theindividual, added compounds are employed in concentrations of 0.005 to6%, preferably 0.1 to 3%. The total concentration of these furtherconstituents is in the range from 0% to 10%, preferably 0.1% to 6%,based on the mixture as a whole. However, the concentration data for theremaining constituents of the liquid-crystal mixtures, i.e. theliquid-crystalline or mesogenic compounds, are indicated without takinginto account the concentration of these additives.

The liquid-crystalline media preferably comprise 0 to 10% by weight, inparticular 0.01 to 5% by weight and particularly preferably 0.1 to 3% byweight, of stabilisers. The media preferably comprise one or morestabilisers selected from 2,6-di-tert-butylphenols,2,2,6,6-tetramethylpiperidines or 2-benzotriazol-2-ylphenols. Theseassistants are known to the person skilled in the art and arecommercially available, for example as light stabilisers.

An embodiment of the invention is therefore also a process for thepreparation of a liquid-crystal medium which is characterised in thatone or more compounds of the formula I are mixed with one or morefurther compounds and optionally with one or more additives. The furthercompounds are preferably selected from the compounds of the formula II,as indicated above, and optionally one or more further compounds.

In the present application, the expression dielectrically positivedescribes compounds or components where Δ∈>3.0, dielectrically neutraldescribes those where −1.5≦Δ∈≦3.0 and dielectrically negative describesthose where Δ∈<−1.5. The dielectric anisotropy of the respectivecompound is determined from the results of a solution of 10% of therespective individual compound in a nematic host mixture. If thesolubility of the respective compound in the host mixture is less than10%, the concentration is reduced to 5%. The capacitances of the testmixtures are determined both in a cell having homeotropic alignment andin a cell having homogeneous alignment. The cell thickness of both typesof cells is approximately 20 μm. The voltage applied is a rectangularwave having a frequency of 1 kHz and an effective value of typically 0.5V to 1.0 V, but it is always selected to be below the capacitivethreshold of the respective test mixture.

Δ∈ is defined as (∈_(∥)−∈_(⊥)), whereas ∈_(average) is (∈_(∥)+2∈_(⊥))/3.

The host mixture used for dielectrically positive compounds is mixtureZLI-4792 and that used for dielectrically neutral and dielectricallynegative compounds is mixture ZLI-3086, both from Merck KGaA, Germany.The absolute values of the dielectric constants of the compounds aredetermined from the change in the respective values of the host mixtureon addition of the compounds of interest. The values are extrapolated toa concentration of the compounds of interest of 100%.

Components having a nematic phase at the measurement temperature of 20°C. are measured as such, all others are treated like compounds.

The term threshold voltage in the present application refers to theoptical threshold and is quoted for 10% relative contrast (V₁₀), and theterm saturation voltage refers to the optical saturation and is quotedfor 90% relative contrast (V₉₀), in both cases unless expressly statedotherwise. The capacitive threshold voltage (V₀), also called theFreedericks threshold (V_(Fr)), is only used if expressly mentioned.

The parameter ranges indicated in this application all include the limitvalues, unless expressly stated otherwise.

The different upper and lower limit values indicated for various rangesof properties in combination with one another give rise to additionalpreferred ranges.

Throughout this application, the following conditions and definitionsapply, unless expressly stated otherwise. All concentrations are quotedin percent by weight and relate to the respective mixture as a whole,all temperatures are quoted in degrees Celsius and all temperaturedifferences are quoted in differential degrees. All physical propertiesthat are typical for liquid crystals are determined in accordance with“Merck Liquid Crystals, Physical Properties of Liquid Crystals”, StatusNovember 1997, Merck KGaA, Germany, and are quoted for a temperature of20° C., unless expressly stated otherwise. The optical anisotropy (Δn)is determined at a wavelength of 589.3 nm. The dielectric anisotropy(Δ∈) is determined at a frequency of 1 kHz. The threshold voltages, aswell as all other electro-optical properties, are determined using testcells produced at Merck KGaA, Germany. The test cells for thedetermination of Δ∈ have a cell thickness of approximately 20 μm. Theelectrode is a circular ITO electrode having an area of 1.13 cm² and aguard ring. The orientation layers are SE-1211 from Nissan Chemicals,Japan, for homeotropic orientation (∈_(∥)) and polyimide AL-1054 fromJapan Synthetic Rubber, Japan, for homogeneous orientation (∈_(⊥)). Thecapacitances are determined using a Solatron 1260 frequency responseanalyser using a sine wave with a voltage of 0.3 V_(rms). The light usedin the electro-optical measurements is white light. A set-up using acommercially available DMS instrument from Autronic-Melchers, Germany,is used here. The characteristic voltages are determined underperpendicular observation. The threshold (V₁₀), mid-grey (V₅₀) andsaturation (V₉₀) voltages are determined for 10%, 50% and 90% relativecontrast, respectively.

The liquid-crystalline media are investigated with respect to theirproperties in the microwave frequency range as described in A.Penirschke et al. “Cavity Perturbation Method for Characterization ofLiquid Crystals up to 35 GHz”, 34^(th) European MicrowaveConference—Amsterdam, pp. 545-548. Compare in this respect also A.Gaebler et al. “Direct Simulation of Material Permittivities . . . ”,12MTC 2009—International Instrumentation and Measurement TechnologyConference, Singapore, 2009 (IEEE), pp. 463-467, and DE 10 2004 029 429A, in which a measurement method is likewise described in detail.

The liquid crystal is introduced into a polytetrafluoroethylene (PTFE)or quartz capillary. The capillary has an internal radius of 180 μm andan external radius of 350 μm. The effective length is 2.0 cm. The filledcapillary is introduced into the centre of the cavity with a resonancefrequency of 30 GHz. This cavity has a length of 6.6 mm, a width of 7.1mm and a height of 3.6 mm. The input signal (source) is then applied,and the result of the output signal is recorded using a commercialvector network analyser. For other frequencies (e.g. 19 GHz), thedimensions of the cavity are adapted correspondingly.

The change in the resonance frequency and the Q factor between themeasurement with the capillary filled with the liquid crystal and themeasurement without the capillary filled with the liquid crystal is usedto determine the dielectric constant and the loss angle at thecorresponding target frequency by means of equations 10 and 11 in theabove-mentioned publication A. Penirschke et al., 34^(th) EuropeanMicrowave Conference—Amsterdam, pp. 545-548, as described therein.

The values for the components of the properties perpendicular andparallel to the director of the liquid crystal are obtained by alignmentof the liquid crystal in a magnetic field. To this end, the magneticfield of a permanent magnet is used. The strength of the magnetic fieldis 0.35 tesla. The alignment of the magnet is set correspondingly andthen rotated correspondingly through 90°.

The dielectric anisotropy in the microwave range is defined asΔ∈_(r)≡(∈_(r,∥)−∈_(r,⊥)).

The modulatability or tuneability (τ) is defined asτ≡(Δ∈_(r)/∈_(r,∥)).

The material quality (η) is defined asη≡(τ/tan δ_(∈) _(r,max.) ),with the maximum dielectric loss factor tan δ_(∈) _(r,max.) :tan δ_(∈) _(r,max.) ≡max. {tan δ_(∈) _(r,⊥) ;tan δ_(∈) _(r,∥) }which arises from the maximum value of the measured values for tanδ_(∈r).

The material quality (η) of the preferred liquid-crystal materials is 6or more, preferably 8 or more, preferably 10 or more, preferably 15 ormore, preferably 17 or more, particularly preferably 20 or more and veryparticularly preferably 25 or more.

In the corresponding components, the preferred liquid-crystal materialshave phase shifter qualities of 15°/dB or more, preferably 20°/dB ormore, preferably 30°/dB or more, preferably 40°/dB or more, preferably50°/dB or more, particularly preferably 80°/dB or more and veryparticularly preferably 100°/dB or more.

The liquid-crystal media according to the invention preferably havenematic phases of in each case at least from −20° C. to 80° C.,preferably from −30° C. to 85° C. and very particularly preferably from−40° C. to 100° C. The phase particularly preferably extends to 120° C.or more, preferably to 140° C. or more and very particularly preferablyto 180° C. or more. The expression have a nematic phase here means onthe one hand that no smectic phase and no crystallisation are observedat low temperatures at the corresponding temperature and on the otherhand that no clearing occurs on heating from the nematic phase. Theinvestigation at low temperatures is carried out in a flow viscometer atthe corresponding temperature and checked by storage in test cellshaving a cell thickness of 5 μm for at least 100 hours. At hightemperatures, the clearing point is measured in capillaries byconventional methods.

The liquid-crystal media in accordance with the present inventionpreferably have a clearing point of 90° C. or more, more preferably 100°C. or more, even more preferably 120° C. or more, particularlypreferably 150° C. or more and very particularly preferably 170° C. ormore.

The Δ∈ of the liquid-crystal medium in accordance with the invention, at1 kHz and 20° C., is preferably 1 or more, more preferably 2 or more andvery preferably 3 or more.

The Δn of the liquid-crystal media in accordance with the presentinvention, at 589 nm (Na^(D)) and 20° C., is preferably in the rangefrom 0.20 or more to 0.90 or less, more preferably in the range from0.25 or more to 0.90 or less, even more preferably in the range from0.30 or more to 0.85 or less and very particularly preferably in therange from 0.35 or more to 0.80 or less.

In a preferred embodiment of the present application, the Δn of theliquid-crystal media in accordance with the present invention is 0.45 ormore, preferably 0.50 or more, and particularly preferably 0.55 or more.

Furthermore, the liquid-crystal media according to the invention arecharacterised by high anisotropies in the microwave range. Thebirefringence is, for example, preferably 0.14 or more, particularlypreferably 0.15 or more, particularly preferably 0.20 or more,particularly preferably 0.25 or more and very particularly preferably0.30 or more, at about 8.3 GHz. In addition, the birefringence ispreferably 0.80 or less.

The liquid crystals employed are either individual substances ormixtures. They preferably have a nematic phase.

In the present application, the term compounds means both one compoundand a plurality of compounds, unless expressly stated otherwise.

Preferred components which comprise a liquid-crystal medium or at leastone compound in accordance with the invention are phase shifters,varactors, antenna arrays (for example for radio, mobile communications,microwave/radar and other data transmission), ‘matching circuit adaptivefilters’ and others. Preference is given to components forhigh-frequency technology, as defined above. Preference is also given tocomponents which can be modulated by different applied electricalvoltages. Very particularly preferred components are phase shifters. Inpreferred embodiments, a plurality of phase shifters are functionallyconnected, giving, for example, a phase-controlled group antenna,generally referred to as ‘phased array’ antenna. A group antenna usesthe phase shift of the transmitting or receiving elements arranged in amatrix in order to achieve bundling through interference. A parallelarrangement of phase shifters in row or grid form enables theconstruction of a so-called ‘phased array’, which can serve as tuneabletransmitting or receiving antenna for high frequencies (for examplegigahertz range). Phased array antennae according to the invention havea very broad usable reception cone.

Preferred applications are radar installations and data transmissionequipment on manned or unmanned vehicles from the automobile, shipping,aircraft, space travel and satellite technology areas.

For the production of suitable components, in particular phase shifters,a liquid-crystalline medium according to the invention is typicallyintroduced into rectangular cavities having a thickness of less than 1mm, a width of several mm and a length of several centimeters. Thecavities have opposing electrodes mounted along two long sides. Sucharrangements are familiar to the person skilled in the art. Throughapplication of a variable voltage, the dielectric properties of theliquid-crystalline medium can be tuned during operation of the antennain order to set different frequencies or directions of an antenna.

The term “halogen” or “halogenated” stands for F, Cl, Br and I,particularly for F and Cl and in particular for F.

The term “alkyl” preferably encompasses straight-chain and branchedalkyl groups having 1 to 15 carbon atoms, in particular thestraight-chain groups methyl, ethyl, propyl, butyl, pentyl, hexyl andheptyl. Groups having 2 to 10 carbon atoms are generally preferred.

The term “alkenyl” preferably encompasses straight-chain and branchedalkenyl groups having 2 to 15 carbon atoms, in particular thestraight-chain groups. Particularly preferred alkenyl groups are C₂- toC₇-1E-alkenyl, C₄- to C₇-3E-alkenyl, C₅- to C₇-4-alkenyl, C₆- toC₇-5-alkenyl and C₇-6-alkenyl, in particular C₂- to C₇-1E-alkenyl, C₄-to C₇-3E-alkenyl and C₅- to C₇-4-alkenyl. Examples of further preferredalkenyl groups are vinyl, 1E-propenyl, 1E-butenyl, 1E-pentenyl,1E-hexenyl, 1E-heptenyl, 3-butenyl, 3E-pentenyl, 3E-hexenyl,3E-heptenyl, 4-pentenyl, 4Z-hexenyl, 4E-hexenyl, 4Z-heptenyl, 5-hexenyl,6-heptenyl and the like. Groups having up to 5 carbon atoms aregenerally preferred.

The term “alkoxy” preferably encompasses straight-chain radicals of theformula C_(n)H_(2n+1)—O—, in which n denotes 1 to 10. n is preferably 1to 6. Preferred alkoxy groups are, for example, methoxy, ethoxy,n-propoxy, n-butoxy, n-pentoxy, n-hexoxy, n-heptoxy, n-octoxy, n-nonoxy,n-decoxy.

The term “oxaalkyl” or “alkoxyalkyl” preferably encompassesstraight-chain radicals of the formula C_(n)H_(2n+1)—O—(CH₂)_(m), inwhich n and m each, independently of one another, denote 1 to 10.Preferably, n is 1 and m is 1 to 6.

The term “fluorinated alkyl radical” preferably encompasses mono- orpolyfluorinated radicals. Perfluorinated radicals are included.Particular preference is given to CF₃, CH₂CF₃, CH₂CHF₂, CHF₂, CH₂F,CHFCF₃ and CF₂CHFCF₃.

The term “fluorinated alkoxy radical” encompasses mono- orpolyfluorinated radicals. Perfluorinated radicals are preferred.Particular preference is given to the OCF₃ radical.

The term “substituted cycloalkyl” encompasses cycloalkyl which is mono-or polysubstituted by alkyl, in particular alkyl having 1 to 8 carbonatoms.

The term “substituted phenyl” encompasses phenyl which is mono- orpolysubstituted by a group defined like R¹, in particular phenyl whichis substituted by F, Cl, alkyl or alkoxy.

In the present application, high-frequency technology means applicationshaving frequencies in the range from 1 MHz to 10 THz, preferably from 1GHz to 3 THz, more preferably from 2 GHz to 1 THz, particularlypreferably from 5 to 300 GHz. The application is preferably in themicrowave spectrum or adjacent regions which are suitable for messagetransmission, in which phased array modules can be used in transmittingor receiving antennae.

The liquid-crystal media according to the invention consist of one ormore compounds, preferably 2 to 30, more preferably 3 to 20 and verypreferably 3 to 16, compounds. These compounds are mixed in aconventional manner. In general, the desired amount of the compound usedin the smaller amount is dissolved in the compound used in the largeramount. If the temperature is above the clearing point of the compoundused in the higher concentration, it is particularly easy to observecompletion of the dissolution process. It is, however, also possible toprepare the media in other conventional ways, for example usingso-called pre-mixes, which can be, for example, homologous or eutecticmixtures of compounds, or using so-called “multibottle” systems, theconstituents of which are themselves ready-to-use mixtures.

All temperatures, such as, for example, the melting point T(C,N) orT(C,S), the transition from the smectic (S) to the nematic (N) phaseT(S,N) and the clearing point T(N,I) of the liquid crystals, are quotedin degrees Celsius. All temperature differences are quoted indifferential degrees.

In the present application and in the following examples, the structuresof the liquid-crystal compounds are indicated by means of acronyms,where the transformation into chemical formulae is carried out inaccordance with Tables A and B below. All radicals C_(n)H_(2n+1) andC_(m)H_(2m+1) are straight-chain alkyl radicals having n and m C atomsrespectively; n, m and k are integers and preferably denote 0, 1, 2, 3,4, 5, 6, 7, 8, 9, 10, 11 or 12. The coding in Table B is self-evident.In Table A, only the acronym for the parent structure is indicated. Inindividual cases, the acronym for the parent structure is followed,separated by a dash, by a code for the substituents R^(1*), R^(2*),L^(1*) and L^(2*):

Code for R¹*, R²*, L¹*, L²*, L³* R¹* R²* L¹* L²* nm C_(n)H_(2n+1)C_(m)H_(2m+1) H H nOm C_(n)H_(2n+1) OC_(m)H_(2m+1) H H nO.mOC_(n)H_(2n+1) C_(m)H_(2m+1) H H n C_(n)H_(2n+1) CN H H nN.FC_(n)H_(2n+1) CN F H nN.F.F C_(n)H_(2n+1) CN F F nF C_(n)H_(2n+1) F H HnCl C_(n)H_(2n+1) Cl H H nOF OC_(n)H_(2n+1) F H H nF.F C_(n)H_(2n+1) F FH nF.F.F C_(n)H_(2n+1) F F F nOCF₃ C_(n)H_(2n+1) OCF₃ H H nOCF₃.FC_(n)H_(2n+1) OCF₃ F H n-Vm C_(n)H_(2n+1) —CH═CH—C_(m)H_(2m+1) H H nV-VmC_(n)H_(2n+1)—CH═CH— —CH═CH—C_(m)H_(2m+1) H H

Suitable mixture components are given in Tables A and B.

TABLE A

BCH

CBC

CCH

CCP

CPTP

CEPTP

ECCP

CECP

EPCH

PCH

CH

PTP

CCPC

CP

BECH

TABLE B

CBC-nmF

PGP-n-m

CGG-n-F

CPGP-n-m

PPGU-n-F

GGP-n-F

PGIGI-n-F

The following examples illustrate the present invention without limitingit in any way.

However, it becomes clear to the person skilled in the art from thephysical properties what properties can be achieved and in what rangesthey can be modified. In particular, the combination of the variousproperties which can preferably be achieved is thus well defined for theperson skilled in the art.

Abbreviations used:

-   DMPU 1,3-dimethyl-3,4,5,6-tetrahydro-2(1H)-pyrimidinone-   DBU 1,8-diazabicyclo[5.4.0]undec-7-ene or    2,3,4,6,7,8,9,10-octahydropyrimido[1,2-a]azepine (IUPAC)

EXAMPLES

The acetylenes and boronic acids employed are commercially available orcan be prepared analogously to Schemes I to VIII or to known syntheses.The radicals “C₄H₉” stand for unbranched n-butyl radicals. Acorresponding situation applies to C₃H₇, C₆H₁₃, etc.

Synthesis Example 1

Step 1.1

25.4 g of 2-bromo-1,4-dichlorobenzene, 8.9 ml of iodoethane and 13.3 mlof DMPU are dissolved in 230 ml of THF, and a solution of 16.2 g oflithium tetramethylpiperidide in THF is added dropwise at −70° C. Aftera further 2 h at −70° C., the reaction mixture is allowed to warm toambient temperature, and the batch is hydrolysed using water and workedup by extraction. The crude product is purified by fractionaldistillation.

b.p.: 73° C./0.1 bar. Colourless liquid.

Step 1.2

12.5 ml of a 5% solution of methyllithium in diethyl ether are added to2.4 g of anhydrous zinc bromide in 50 ml of THF at 25-40° C. 0.3 g ofPdCl₂— dppf, bis(diphenylphosphinoferrocene)palladium dichloride, isthen added, the mixture is heated to the boil, and 4.6 g of the productfrom step 1.1, dissolved in a little THF, are added dropwise. Thereaction mixture is subsequently heated under reflux for 15 h. The batchis hydrolysed using water and worked up by extraction. The crude productis purified by chromatography (pentane/silica gel). Colourless liquid.

Step 1.3

2.4 g of 4-butylphenylacetylene are initially introduced in 30 ml of THFand cooled to −78° C. 14.3 ml of a 1 M solution of lithiumbis(trimethylsilyl)amide in hexane are added dropwise to this solution,and the mixture is allowed to react at −78° C. for a further 1 h. 14.3ml of a 1 M solution of methoxy-9-BBN are then added dropwise, and themixture is stirred at −78° C. for a further 2 h. In a second apparatus,1.0 g of the product from the last step, dissolved in 40 ml of THF, isinitially introduced with the catalyst comprising 0.2 g oftris(dibenzylideneacetone)dipalladium and 0.35 g of2-dicyclohexylphosphino-2′,6′-dimethoxybiphenyl, and the reactionsolution from the first reaction is added at room temperature. Themixture is heated at the boil for 15 h. The batch is hydrolysed usingwater and worked up by extraction. The crude product is purified bychromatography (pentane/silica gel). Recrystallisation from pentanegives the purified title product.

C 45 N 180 I

Δ∈=+1.4

Δn=0.412

Comparative Example 1

C 29 N 119 IΔ∈=+1.7Δn=0.402

Synthesis Example 2

The compound is prepared analogously to Example 1.

C 118 N 222 I

Δ∈=+2.6

Δn=0.435

γ₁=889 mPa·s

Synthesis Example 3

The compound is prepared analogously to Example 1.

C 167 N 225 I

Δ∈=+2.3

Δn=0.423

γ₁=1361 mPa·s

Synthesis Example 4

The compound is prepared analogously to Example 1.

C 90 N 194 I

Δ∈=+3.0

Δn=0.435

γ₁=647 mPa·s

Comparative Example 2

C 93 N 188.5 IΔ∈4.1Δn 0.452γ₁=374 mPa·s

Synthesis Example 5

The compound is prepared analogously to Example 1.

C 96 N 199 I

Δ∈=−1.4

Δn=0.443

γ₁=308 mPa·s

Synthesis Example 6

The compound is prepared analogously to Example 1.

C 92 N 205 I

Δ∈=+3.1

Δn=0.429

Synthesis Example 7

The compound is prepared analogously to Example 1.

C 53 N 144 I

Δ∈=+2.5

Δn=0.401

γ₁=1746 mPa·s

Comparative Example 3

C 60 N 122 IΔ∈=+1.7Δn=0.394γ₁=1891 mPa·s

Synthesis Example 8

Compound (1) is prepared analogously to Example 1 and used in MixtureExample 1.

Tg −49 C 32 N 126 I

Δ∈=+1.6

Δn=0.373

γ₁=1269 mPa·s

Comparative Example 4

C 72 N 84.5 IΔ∈=+1.5Δn=0.378γ₁=2194 mPa·s

Synthesis Example 9

The title compound is prepared analogously to Example 1.

C 60 N 89 I

Δ∈=+1.3

Δn=0.348

γ₁=1875 mPa·s

Comparative Example 5

Tg −39 C 69 N 70 IΔ∈ 0.9Δn 0.359γ₁ 3067 mPa·s

Synthesis Example 10

The title compound is prepared analogously to Example 1.

C 80 N 192 I

Δ∈=−0.9

Δn=0.426

γ₁=508 mPa·s

Synthesis Example 11

The title compound is prepared analogously to Example 1.

C 41 N 161 I

Δ∈=2.4

Δn=0.437

Synthesis Example 12

The title compound is prepared analogously to Example 1.

C 48 N 159 I

Synthesis Example 13

The title compound is prepared analogously to Example 1.

Tg −37 C 52 N 78 I

Δ∈=0.9

Δn=0.339

γ₁=2219 mPa·s

Synthesis Example 14

The title compound is prepared analogously to Example 1.

Tg −34 C 72 N (49) I

Δ∈=0.8

Δn=0.302

γ₁=785 mPa·s

Synthesis Example 15

The title compound is prepared analogously to Example 1.

C 97 N 204 I

Δ∈=−0.9

Δn=0.421

γ₁=610 mPa·s

Synthesis Example 16

The title compound is prepared analogously to Example 1.

C 72 N (51) I

Mixture Example 1

A liquid-crystal medium M-1 having the composition and properties asindicated in the following table is prepared. Compound (1) (No. 15)originates from Synthesis Example 8.

Composition Compound No. Abbreviation 1 BCH-3F.F 10.8% 2 BCH-5F.F 9.00%3 ECCP-30CF3 4.50% 4 ECCP-50CF3 4.50% 5 CBC-33F 1.80% 6 CBC-53F 1.80% 7CBC-55F 1.80% 8 PCH-6F 7.20% 9 PCH-7F 5.40% 10 CCP-20CF3 7.20% 11CCP-30CF3 10.8% 12 CCP-40CF3 6.30% 13 CCP-50CF3 9.90% 14 PCH-5F 9.00% 15(1) 10.0% Σ 100.0% Physical properties T(N, I) = 96° C. Δn (20° C.,589.3 nm) = 0.124 Δε (20° C., 1 kHz) = 4.9  γ₁ (20° C.) = 166 mPa · s

This mixture is used for applications in the microwave range, inparticular for phase shifters for ‘phased array’ antennae.

For comparison, a medium C-1 without component (1) is prepared fromcompound Nos. 1-14 of medium M-1, where compound Nos. 1-14 are presentin the same relative amounts.

TABLE Properties of mixtures M-1 and C-2 (comparison) at 19 GHz (20° C.)Mixture ε_(r,||) ε_(r,⊥) τ tan δ_(ε,r,||) tan δ_(ε,r,⊥) η M-1 2.57 2.330.097 0.0044 0.0130 7.41 C-1 2.49 2.30 0.079 0.0048 0.0139 5.70

The tuneability τ and the material quality η are improved compared withcomparative mixture C-1.

Further combinations of the embodiments and variants of the invention inaccordance with the description also arise from the following claims.

The invention claimed is:
 1. A compound of the formula I

in which A³ denotes

L¹ denotes branched or unbranched alkyl, alkenyl or alkynyl having 1 to12 C atoms, in which, in addition, one or more —CH₂— groups may bereplaced, independently of one another, by O, substituted orunsubstituted cycloalkyl, cycloalkenyl, substituted or unsubstitutedphenyl, substituted or unsubstituted arylethynyl, fluorinated alkyl oralkenyl, or fluorinated alkoxy or alkenyloxy, or L¹ denotes F, Cl, Br,CN, NCS or SF₅, L² denotes branched or unbranched alkyl, alkenyl oralkynyl having 1 to 12 C atoms, in which, in addition, one or more —CH₂—groups may be replaced, independently of one another, by O, substitutedor unsubstituted cycloalkyl, cycloalkenyl, substituted or unsubstitutedphenyl, substituted or unsubstituted arylethynyl, fluorinated alkyl oralkenyl, fluorinated alkoxy or alkenyloxy, L³ and L⁴ independently areas defined for L¹ or denote H, R¹ and R², independently of one another,denote a halogenated or unsubstituted alkyl radical having 1 to 15 Catoms, where, in addition, one or more CH₂ groups in these radicals mayeach be replaced, independently of one another, by —C≡C—, —CH═CH—,—CF═CF—, —CF═CH—, —CH═CF—, —(CO)— and —O— in such a way that O atoms arenot linked directly to one another, or denote F, Cl, Br, CN, CF₃, OCF₃,NCS or SF₅, or R² can also denote H, A¹, A², A⁴ and A⁵ each,independently of one another, denote a) 1,4-phenylene, in which one ormore CH groups may be replaced by N, b) trans-1,4-cyclohexylene orcyclohexenylene, in which, in addition, one or two non-adjacent CH₂groups may be replaced by —O— and/or —S—, and in which H may be replacedby F, c) a radical of the formula

or d) a radical selected from 1,4-bicyclo[2.2.2]octylene,cyclo-butane-1,3-diyl, spiro[3.3]heptane-2,6-diyl, thiophene-2,5-diyl,thiophene-2,4-diyl, furan-2,5-diyl, furan-2,4-diyl,

and in which, in groups a), b), c) and d), one or more H atoms may, inaddition, be replaced by Br, Cl, F, CN, —NCS, —SCN, SF₅, C₁-C₁₀ alkyl,C₁-C₁₀ alkoxy or a mono- or polyfluorinated C₁-C₁₀ alkyl or alkoxygroup, k denotes 0 or 1, Z¹ and Z⁵, independently of one another, denotea single bond, —C≡C—, —CH═CH—, —CH₂O—, —(CO)O—, —CF₂O—, —CF₂CF₂—,—CH₂CF₂—, —CH₂CH₂—, —(CH₂)₄—, —CH═CF— or —CF═CF—, where asymmetricalbridges may be oriented to both sides, where, for k=0, Z⁵ is a singlebond, and m and n, independently of one another, denote 0, 1 or
 2. 2. Acompound according to claim 1, wherein L³ and L⁴ both denote H or bothdo not denote H.
 3. A compound according to claim 1, wherein L¹ denotesF.
 4. A compound according to claim 1, wherein L¹ and/or L²independently denote a halogenated or unsubstituted alkyl radical having1 to 12 C atoms, where, in addition, one or more CH₂ groups in theseradicals may each be replaced, independently of one another, by —C≡C—,—CH═CH—, —CF═CF—, —CF═CH—, —CH═CF—, —(CO)O—, —O(CO)—, —(CO)—, —O— or —S—in such a way that O or S atoms are not linked directly to one another,optionally alkyl-substituted cycloalkyl having 3 to 6 C atoms, oroptionally halogen-, C₁₋₆-alkyl- or C₁₋₆-alkoxy-substituted phenyl.
 5. Acompound according to claim 1, wherein m and n are
 0. 6. A compoundaccording to claim 1, wherein k is
 1. 7. A liquid-crystal medium, whichcomprises one or more compounds of the formula I according to claim 1.8. A liquid-crystal medium according to claim 7, which additionallycomprises one or more compounds selected from the compounds of theformula II:

in which: L¹¹ denotes R¹¹ or X¹¹, L¹² denotes R¹² or X¹², R¹¹ and R¹²,independently of one another, denote unfluorinated alkyl orunfluorinated alkoxy having 1 to 17 C atoms or unfluorinated alkenyl,unfluorinated alkynyl, unfluorinated alkenyloxy or unfluorinatedalkoxyalkyl having 2 to 15 C atoms, X¹¹ and X¹², independently of oneanother, denote F, Cl, Br, —CN, —NCS, —SCN, —SF₅, fluorinated alkyl orfluorinated alkoxy having 1 to 7 C atoms or fluorinated alkenyl,fluorinated alkenyloxy or fluorinated alkoxyalkyl having 2 to 7 C atoms,p and q independently denote 0 or 1, Z¹¹ to Z¹³, independently of oneanother, denote trans-CH═CH—, trans-CF═CF—, —C≡C— or a single bond, and

independently of one another, denote

where R¹³ denotes Cl, C₁₋₅ alkyl, C₁₋₅ alkenyl or C₃₋₆ cycloalkyl.
 9. Aliquid-crystal medium according to claim 7, wherein the concentration ofthe compounds of the formula I in the medium is in the range from intotal 5% to 95%.
 10. A component for high-frequency technology,comprising at least one compound of the formula I according to claim 1.11. A process for the preparation of a liquid-crystal medium accordingto claim 7, which comprises mixing one or more compounds of the formulaI with one or more further compounds and optionally with one or moreadditives.
 12. A component for high-frequency technology, whichcomprises a liquid-crystal medium according to claim
 7. 13. A componentaccording to claim 12, which is one or more functionally connected phaseshifters.
 14. A phased array antenna which comprises one or morecomponents according to claim 12.